In the Debye model, Planck's constant times this quantity divided by wavele
In the Debye model, Planck's constant times this quantity divided by wavelength gives the vibrational energy of phonons in a crystal. At it, one may observe a Prandtl-Glauert Singularity, or "shock egg" from a white cylindrical cone of water droplets due to a decrease in [*] air pressure. The ThrustSSC and Bell XS-1 achieved it, on land and air respectively. For 10 points, name this point at which an object travels with a Mach number greater than one, and moves from transonic to supersonic speed.
In the Debye model, Planck's constant times this quantity divided by wavelength gives the vibrational energy of phonons in a crystal.
speed of {sound} [accept {sound barrier}; accept {c}-{sub}-{s}; prompt "{Mach 1}" before mentioned]